Stacked Quad 57s were hardly the brainchild of Mark Levinson or whosis. I am 10 years older than you, and I first heard stacked Quads in the home of one of my patients, when I was an intern, in 1970. He drove them with a Marantz 7C preamplfier (when the term "preamplifier" automatically meant built in phono stage) and Marantz 9 amplifiers. Harmony House in Manhattan also had them back then. Mark Levinson was a kid at that point in time. He can take credit for the HQD system, I agree. What you are not hearing me say is that the stacked Quad 57 system that I heard locally a few years ago was comprised of speakers wherein the onboard electronics, courtesy of Peter Walker in his attempt to turn them into a point source, were gutted and so too was the OEM audio transformer. In place of that stuff, Dave Slagle devised a tube amplifier with an output transformer that could directly drive the panel. In other words, only one transformer at the interface. And that transformer can have wider bandwidth and lower distortion than typical transformers used to couple tube amplifiers to ESLs, because the ratio of the two impedances, the output impedance of the tube output stage (which is very high, not like our OTLs that are designed to have a low output Z) vs the input impedance of the panels, are more nearly the same. Plus, Dave wound it himself. Like I also said, that system, owned by a local guy and unique in the world so far as I know unless Dave has built one or two for others, can play very loud and with very low distortion and may in fact incorporate a subwoof in its base. Like I also said, I have many hours listening to my friend’s Acoustat 2+2s. There is no contest at all. As I also said before, the guy who owns the aforementioned system uses stacked Quad 57 triplets at home, but he only saw fit to bring the doublet to CAF. So, you have a system with markedly enhanced durability in its ability to play at high SPLs and bandwidth, with reduced distortion even below that of the base Quad 57. It’s awesome; trust me.
Oh yeah, the reason the Sanders ESL amplifier is so large is because it has to develop the voltage to drive an ESL. Most SS amplifiers are good at current (i.e., driving low impedance speakers) but not so good at voltage. ESLs require voltage except at very high frequencies, which is why in general a tube amp is a superior match. OTLs are better yet, of course.
